Sister Yua has a slightly strong personality and tends to be a bit spoiled when things don't go her way. In contrast, younger sister Chiharu is gentle and easily swayed by others' opinions. The two were casually drinking tea together in the living room when Chiharu complained that her boyfriend's sex was too intense, causing her some distress. Hearing this, Yua felt a twinge of envy and began growing curious about her sister's boyfriend. Boldly, Yua proposed, "How about we swap boyfriends?" A new shift begins to unfold in their relationship.